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+                    GNU GENERAL PUBLIC LICENSE
+                       Version 3, 29 June 2007
+
+ Copyright (C) 2007 Free Software Foundation, Inc. <https://fsf.org/>
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+  IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS
+THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY
+GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
+USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
+DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
+PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
+EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
+SUCH DAMAGES.
+
+  17. Interpretation of Sections 15 and 16.
+
+  If the disclaimer of warranty and limitation of liability provided
+above cannot be given local legal effect according to their terms,
+reviewing courts shall apply local law that most closely approximates
+an absolute waiver of all civil liability in connection with the
+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
+
+                     END OF TERMS AND CONDITIONS
+
+            How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    <one line to give the program's name and a brief idea of what it does.>
+    Copyright (C) <year>  <name of author>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+Also add information on how to contact you by electronic and paper mail.
+
+  If the program does terminal interaction, make it output a short
+notice like this when it starts in an interactive mode:
+
+    <program>  Copyright (C) <year>  <name of author>
+    This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+    This is free software, and you are welcome to redistribute it
+    under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License.  Of course, your program's commands
+might be different; for a GUI interface, you would use an "about box".
+
+  You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU GPL, see
+<https://www.gnu.org/licenses/>.
+
+  The GNU General Public License does not permit incorporating your program
+into proprietary programs.  If your program is a subroutine library, you
+may consider it more useful to permit linking proprietary applications with
+the library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.  But first, please read
+<https://www.gnu.org/licenses/why-not-lgpl.html>.
+

README.md

@@ -1,2 +1,138 @@
-# ScuroLogger (slog)
+# slog
 
+Small structured logger for Go with text and JSON output, multiple writers, and optional traceback metadata.
+
+Russian version: [README_ru.md](README_ru.md)
+
+## Features
+
+- Fan out the same record to multiple destinations.
+- Text and JSON writers.
+- `stdout`, files, and arbitrary external `io.Writer` values.
+- Optional timestamps for text output.
+- Compact traceback metadata for text writers and full traceback slices for JSON.
+- Explicit ownership rules for writer closing.
+
+## Installation
+
+```bash
+go get git.nix13.pw/scuroneko/slog
+```
+
+## Quick start
+
+```go
+package main
+
+import (
+	"log"
+
+	"git.nix13.pw/scuroneko/slog"
+)
+
+func main() {
+	logger := slog.CreateLogger().
+		Prefix("API").
+		Level(slog.DEBUG).
+		PrintTraceback(true).
+		JsonPretty(true)
+
+	text := logger.CreateTextStdoutWriter()
+	jsonFile, err := logger.CreateJsonFileWriter("logs/app.json")
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	logger.AddWriters(text, jsonFile)
+
+	logger.Infoln("service started")
+	logger.Warnln("cache miss")
+	logger.Errorln("request failed")
+	logger.Debugln("debug details")
+
+	if err := logger.Close(); err != nil {
+		log.Fatal(err)
+	}
+}
+```
+
+## Defaults
+
+`CreateLogger()` starts with:
+
+- `Prefix("LOG")`
+- `Level(slog.FATAL)`
+- `PrintTime(true)`
+- `PrintTraceback(false)`
+- `JsonPretty(false)`
+
+Important: with the current level ordering, `Level(slog.FATAL)` allows `INFO`, `WARN`, `ERROR`, and `FATAL`, but not `DEBUG`. Use `Level(slog.DEBUG)` to enable every level.
+
+## Writers and ownership
+
+`Logger.Close()` only closes writers created by the logger itself:
+
+- `CreateTextFileWriter(...)`
+- `CreateJsonFileWriter(...)`
+
+The following writers remain owned by the caller and are not closed by `Logger.Close()`:
+
+- `CreateTextWriter(existingWriter)`
+- `CreateJsonWriter(existingWriter)`
+- `CreateTextStdoutWriter()`
+- `CreateJsonStdoutWriter()`
+
+This makes it safe to plug in `bytes.Buffer`, network writers, and other externally managed resources.
+
+## Output formats
+
+Text writers render records like:
+
+```text
+[API] [INFO] [main.go:main:27] [17.03.26 14:05:09] service started
+```
+
+The traceback field is included only when `PrintTraceback(true)` is enabled.
+
+JSON writers emit objects with this shape:
+
+```json
+{
+  "time": "2026-03-17T14:05:09.123456789+03:00",
+  "level": "info",
+  "prefix": "API",
+  "message": "service started",
+  "traceback": [
+    {
+      "method": "main",
+      "filename": "main.go",
+      "line": 27,
+      "signature": "main.main",
+      "fullPath": "/path/to/main.go"
+    }
+  ]
+}
+```
+
+When `JsonPretty(true)` is enabled, JSON is indented.
+
+## API summary
+
+- `Info`, `Warn`, `Error`, `Debug`, and `Fatal` accept a list of values.
+- `Infof`, `Warnf`, `Errorf`, `Debugf`, and `Fatalf` use `fmt.Sprintf`.
+- The `*ln` methods preserve newline semantics, which is useful for `stdout`, Docker, and line-based collectors.
+- `Fatal`, `Fatalf`, and `Fatalln` call `os.Exit(1)` after writing the message.
+
+## Traceback behavior
+
+- Text writers use the nearest user stack frame.
+- JSON writers receive the full traceback slice.
+- Internal `slog` frames and `runtime` frames are filtered out.
+
+## Repository example
+
+See [examples/main.go](examples/main.go).
+
+## License
+
+This project is licensed under GNU GPLv3. See [LICENSE](LICENSE).

README_ru.md

@@ -0,0 +1,138 @@
+# slog
+
+Небольшой структурированный логгер для Go с текстовым и JSON-выводом, несколькими writer'ами и настраиваемыми traceback-метаданными.
+
+English version: [README.md](README.md)
+
+## Возможности
+
+- Одновременная запись в несколько destinations.
+- Текстовый и JSON-форматы.
+- `stdout`, файлы и любые внешние `io.Writer`.
+- Опциональные timestamp'ы для текстового вывода.
+- Компактный traceback для текстовых writer'ов и полный traceback для JSON.
+- Явные правила владения writer'ами при `Close()`.
+
+## Установка
+
+```bash
+go get git.nix13.pw/scuroneko/slog
+```
+
+## Быстрый старт
+
+```go
+package main
+
+import (
+	"log"
+
+	"git.nix13.pw/scuroneko/slog"
+)
+
+func main() {
+	logger := slog.CreateLogger().
+		Prefix("API").
+		Level(slog.DEBUG).
+		PrintTraceback(true).
+		JsonPretty(true)
+
+	text := logger.CreateTextStdoutWriter()
+	jsonFile, err := logger.CreateJsonFileWriter("logs/app.json")
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	logger.AddWriters(text, jsonFile)
+
+	logger.Infoln("service started")
+	logger.Warnln("cache miss")
+	logger.Errorln("request failed")
+	logger.Debugln("debug details")
+
+	if err := logger.Close(); err != nil {
+		log.Fatal(err)
+	}
+}
+```
+
+## Значения по умолчанию
+
+`CreateLogger()` создает логгер со следующими настройками:
+
+- `Prefix("LOG")`
+- `Level(slog.FATAL)`
+- `PrintTime(true)`
+- `PrintTraceback(false)`
+- `JsonPretty(false)`
+
+Важно: в текущей модели уровней `Level(slog.FATAL)` пропускает `INFO`, `WARN`, `ERROR` и `FATAL`, но не `DEBUG`. Чтобы включить все сообщения, используйте `Level(slog.DEBUG)`.
+
+## Writer'ы и владение
+
+`Logger.Close()` закрывает только writer'ы, которые логгер создал сам:
+
+- `CreateTextFileWriter(...)`
+- `CreateJsonFileWriter(...)`
+
+Внешние writer'ы не закрываются:
+
+- `CreateTextWriter(existingWriter)`
+- `CreateJsonWriter(existingWriter)`
+- `CreateTextStdoutWriter()`
+- `CreateJsonStdoutWriter()`
+
+Это позволяет безопасно подключать `bytes.Buffer`, сетевые writer'ы и другие уже управляемые ресурсы.
+
+## Форматы вывода
+
+Текстовый writer формирует записи вида:
+
+```text
+[API] [INFO] [main.go:main:27] [17.03.26 14:05:09] service started
+```
+
+Поле traceback появляется только если включен `PrintTraceback(true)`.
+
+JSON writer записывает объект со следующими полями:
+
+```json
+{
+  "time": "2026-03-17T14:05:09.123456789+03:00",
+  "level": "info",
+  "prefix": "API",
+  "message": "service started",
+  "traceback": [
+    {
+      "method": "main",
+      "filename": "main.go",
+      "line": 27,
+      "signature": "main.main",
+      "fullPath": "/path/to/main.go"
+    }
+  ]
+}
+```
+
+Если включен `JsonPretty(true)`, JSON выводится с отступами.
+
+## API кратко
+
+- `Info`, `Warn`, `Error`, `Debug`, `Fatal` принимают список значений.
+- `Infof`, `Warnf`, `Errorf`, `Debugf`, `Fatalf` используют `fmt.Sprintf`.
+- Методы `*ln` добавляют семантику перевода строки, что удобно для `stdout`, Docker и line-based collectors.
+- `Fatal`, `Fatalf` и `Fatalln` вызывают `os.Exit(1)` после записи сообщения.
+
+## Поведение traceback
+
+- Текстовые writer'ы используют ближайший пользовательский stack frame.
+- JSON writer'ы получают полный traceback.
+- Внутренние frame'ы `slog` и `runtime` фильтруются из traceback.
+
+## Пример из репозитория
+
+См. [examples/main.go](examples/main.go).
+
+## Лицензия
+
+Проект распространяется под GNU GPLv3. См. [LICENSE](LICENSE).

doc.go

@@ -0,0 +1,42 @@
+// Package slog provides a small structured logger that can write the same
+// record to text and JSON outputs.
+//
+// A Logger can fan out records to stdout, files, or any external io.Writer.
+// Text writers can include timestamps and a compact traceback frame. JSON
+// writers always emit a structured traceback slice.
+//
+// CreateLogger uses the following defaults:
+//   - prefix: "LOG"
+//   - level: FATAL, which enables info, warn, error, and fatal records
+//   - text timestamps: enabled
+//   - text traceback: disabled
+//   - pretty JSON: disabled
+//
+// Call Level(DEBUG) to enable all records, including debug messages.
+//
+// Basic usage:
+//
+//	logger := slog.CreateLogger().
+//		Prefix("API").
+//		Level(slog.DEBUG).
+//		PrintTraceback(true).
+//		JsonPretty(true)
+//
+//	text := logger.CreateTextStdoutWriter()
+//	jsonFile, err := logger.CreateJsonFileWriter("logs/app.json")
+//	if err != nil {
+//		panic(err)
+//	}
+//
+//	logger.AddWriters(text, jsonFile)
+//	logger.Infoln("service started")
+//
+//	if err := logger.Close(); err != nil {
+//		panic(err)
+//	}
+//
+// Writers created with CreateTextFileWriter or CreateJsonFileWriter are owned by
+// the logger and are closed by Logger.Close. Writers created from existing
+// io.Writer values through CreateTextWriter or CreateJsonWriter remain owned by
+// the caller and are not closed by the logger.
+package slog

examples/main.go

@@ -1,21 +1,53 @@
 package main
 
-import "git.nix13.pw/scuroneko/slog"
+import (
+	"bytes"
+	"fmt"
+
+	"git.nix13.pw/scuroneko/slog"
+)
 
 func main() {
-	logger := slog.CreateLogger().JsonPretty(false)
-	defer logger.Close()
-	logger.AddWriter(logger.CreateTextStdoutWriter())
-	f, err := logger.CreateJsonFileWriter("main.log")
+	logger := slog.CreateLogger().
+		Prefix("EXAMPLE").
+		Level(slog.DEBUG).
+		JsonPretty(true)
+
+	textStdout := logger.CreateTextStdoutWriter()
+	jsonStdout := logger.CreateJsonStdoutWriter()
+
+	textFile, err := logger.CreateTextFileWriter("logs/text.log")
 	if err != nil {
 		panic(err)
 	}
-	logger.AddWriter(f)
-	logger.Infoln("Test")
-	logger.Warnln("Test")
-	logger.Errorln("Test")
-	logger.Debugln("Test") // No output
-	logger.Level(slog.DEBUG)
-	logger.Debugln("Test") // Now we have output
-	logger.Fatalln("Test") // Exit code 1
+
+	jsonFile, err := logger.CreateJsonFileWriter("logs/json.log")
+	if err != nil {
+		panic(err)
+	}
+
+	var externalBuffer bytes.Buffer
+	externalText := logger.CreateTextWriter(&externalBuffer)
+	externalJSON := logger.CreateJsonWriter(&externalBuffer)
+
+	logger.AddWriters(
+		textStdout,
+		jsonStdout,
+		textFile,
+		jsonFile,
+		externalText,
+		externalJSON,
+	)
+
+	logger.Infoln("service started")
+	logger.Warnln("cache miss")
+	logger.Errorln("request failed")
+	logger.Debugln("debug details")
+
+	if err := logger.Close(); err != nil {
+		panic(err)
+	}
+
+	fmt.Println("external buffer contents:")
+	fmt.Println(externalBuffer.String())
 }

go.mod

@@ -1,11 +1,11 @@
 module git.nix13.pw/scuroneko/slog
 
-go 1.25
+go 1.26
 
 require github.com/fatih/color v1.18.0
 
 require (
 	github.com/mattn/go-colorable v0.1.14 // indirect
 	github.com/mattn/go-isatty v0.0.20 // indirect
-	golang.org/x/sys v0.40.0 // indirect
+	golang.org/x/sys v0.42.0 // indirect
 )

go.sum

@@ -7,3 +7,4 @@ github.com/mattn/go-isatty v0.0.20/go.mod h1:W+V8PltTTMOvKvAeJH7IuucS94S2C6jfK/D
 golang.org/x/sys v0.6.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.40.0 h1:DBZZqJ2Rkml6QMQsZywtnjnnGvHza6BTfYFWY9kjEWQ=
 golang.org/x/sys v0.40.0/go.mod h1:OgkHotnGiDImocRcuBABYBEXf8A9a87e/uXjp9XT3ks=
+golang.org/x/sys v0.42.0/go.mod h1:4GL1E5IUh+htKOUEOaiffhrAeqysfVGipDYzABqnCmw=

io.go

@@ -5,55 +5,70 @@ import (
 	"os"
 )
 
+// Infof logs a formatted info message.
 func (l *Logger) Infof(format string, args ...any) {
 	l.print(INFO, fmt.Sprintf(format, args...))
 }
+// Info logs an info message.
 func (l *Logger) Info(m ...any) {
 	l.print(INFO, m...)
 }
+// Infoln logs an info message and appends a newline semantic for writers that need it.
 func (l *Logger) Infoln(m ...any) {
 	l.println(INFO, m...)
 }
 
+// Warnf logs a formatted warning message.
 func (l *Logger) Warnf(format string, args ...any) {
 	l.print(WARN, fmt.Sprintf(format, args...))
 }
+// Warn logs a warning message.
 func (l *Logger) Warn(m ...any) {
 	l.print(WARN, m...)
 }
+// Warnln logs a warning message with newline semantic.
 func (l *Logger) Warnln(m ...any) {
 	l.println(WARN, m...)
 }
 
+// Errorf logs a formatted error message.
 func (l *Logger) Errorf(format string, args ...any) {
 	l.print(ERROR, fmt.Sprintf(format, args...))
 }
+// Error logs an error message.
 func (l *Logger) Error(m ...any) {
 	l.print(ERROR, m...)
 }
+// Errorln logs an error message with newline semantic.
 func (l *Logger) Errorln(m ...any) {
 	l.println(ERROR, m...)
 }
 
+// Fatalf logs a formatted fatal message and exits the process with code 1.
 func (l *Logger) Fatalf(format string, args ...any) {
 	l.print(FATAL, fmt.Sprintf(format, args...))
 	os.Exit(1)
 }
+// Fatal logs a fatal message and exits the process with code 1.
 func (l *Logger) Fatal(m ...any) {
 	l.print(FATAL, m...)
 	os.Exit(1)
 }
+// Fatalln logs a fatal message with newline semantic and exits the process with code 1.
 func (l *Logger) Fatalln(m ...any) {
 	l.println(FATAL, m...)
 	os.Exit(1)
 }
 
+// Debugf logs a formatted debug message.
 func (l *Logger) Debugf(format string, args ...any) {
 	l.print(DEBUG, fmt.Sprintf(format, args...))
 }
+// Debug logs a debug message.
 func (l *Logger) Debug(m ...any) {
 	l.print(DEBUG, m...)
 }
+// Debugln logs a debug message with newline semantic.
 func (l *Logger) Debugln(m ...any) {
 	l.println(DEBUG, m...)
 }
@@ -64,12 +79,18 @@ func (l *Logger) print(level LogLevel, m ...any) {
 	if l.level.n < level.n {
 		return
 	}
+	if len(l.writers) == 0 {
+		return
+	}
 
 	tb := getFullTraceback(0)
 	for _, writer := range l.writers {
+		if writer == nil {
+			continue
+		}
 		err := writer.Print(level, l.prefix, tb, m...)
 		if err != nil {
-			l.Error(err)
+			l.reportWriterError(err)
 		}
 	}
 }
@@ -80,12 +101,28 @@ func (l *Logger) println(level LogLevel, m ...any) {
 	if l.level.n < level.n {
 		return
 	}
+	if len(l.writers) == 0 {
+		return
+	}
 
 	tb := getFullTraceback(0)
+	messages := append(append(make([]any, 0, len(m)+1), m...), "\n")
 	for _, writer := range l.writers {
-		err := writer.Print(level, l.prefix, tb, append(m, "\n")...)
+		if writer == nil {
+			continue
+		}
+		err := writer.Print(level, l.prefix, tb, messages...)
 		if err != nil {
-			l.Error(err)
+			l.reportWriterError(err)
 		}
 	}
 }
+
+// reportWriterError writes internal writer failures directly to stderr to avoid
+// re-entering the same logger path that just failed.
+func (l *Logger) reportWriterError(err error) {
+	if err == nil {
+		return
+	}
+	_, _ = fmt.Fprintf(os.Stderr, "[%s] logger writer error: %v\n", l.prefix, err)
+}

logger.go

@@ -1,6 +1,7 @@
 package slog
 
 import (
+	"errors"
 	"fmt"
 	"io"
 	"strings"
@@ -9,6 +10,7 @@ import (
 	"github.com/fatih/color"
 )
 
+// Logger routes log records to one or more configured writers.
 type Logger struct {
 	prefix  string
 	level   LogLevel
@@ -19,16 +21,19 @@ type Logger struct {
 	jsonPretty     bool
 }
 
+// LogLevel describes a logging severity.
 type LogLevel struct {
 	n uint8
 	t string
 	c color.Attribute
 }
 
+// GetName returns the lowercase textual representation of the level.
 func (l *LogLevel) GetName() string {
 	return l.t
 }
 
+// MethodTraceback describes a single stack frame attached to a log entry.
 type MethodTraceback struct {
 	Method    string `json:"method"`
 	Filename  string `json:"filename"`
@@ -37,6 +42,7 @@ type MethodTraceback struct {
 	FullPath  string `json:"fullPath"`
 }
 
+// Predefined log levels.
 var (
 	INFO  = LogLevel{n: 0, t: "info", c: color.FgWhite}
 	WARN  = LogLevel{n: 1, t: "warn", c: color.FgHiYellow}
@@ -45,6 +51,7 @@ var (
 	DEBUG = LogLevel{n: 4, t: "debug", c: color.FgGreen}
 )
 
+// CreateLogger creates a logger with default settings.
 func CreateLogger() *Logger {
 	return &Logger{
 		prefix:         "LOG",
@@ -54,69 +61,91 @@ func CreateLogger() *Logger {
 	}
 }
 
+// Prefix sets the record prefix and returns the logger for chaining.
 func (l *Logger) Prefix(prefix string) *Logger {
 	l.prefix = prefix
 	return l
 }
+// Level sets the maximum enabled level and returns the logger for chaining.
 func (l *Logger) Level(level LogLevel) *Logger {
 	l.level = level
 	return l
 }
+// PrintTraceback enables traceback output for text writers.
 func (l *Logger) PrintTraceback(b bool) *Logger {
 	l.printTraceback = b
 	return l
 }
+// PrintTime enables timestamps for text writers.
 func (l *Logger) PrintTime(b bool) *Logger {
 	l.printTime = b
 	return l
 }
+// JsonPretty enables indented JSON output for JSON writers.
 func (l *Logger) JsonPretty(b bool) *Logger {
 	l.jsonPretty = b
 	return l
 }
+// AddWriters appends multiple writers to the logger.
 func (l *Logger) AddWriters(writers ...LoggerWriter) *Logger {
 	l.writers = append(l.writers, writers...)
 	return l
 }
+// AddWriter appends a single writer to the logger.
 func (l *Logger) AddWriter(writer LoggerWriter) *Logger {
 	l.writers = append(l.writers, writer)
 	return l
 }
+// Close closes all owned writers and returns a joined error, if any.
 func (l *Logger) Close() error {
+	var errs []error
 	for _, writer := range l.writers {
+		if writer == nil {
+			continue
+		}
 		err := writer.Close()
 		if err != nil {
-			l.Error(err)
+			errs = append(errs, err)
 		}
 	}
-	return nil
+	l.writers = nil
+	return errors.Join(errs...)
 }
 
+// CreateTextWriter wraps an external writer with the logger text settings.
 func (l *Logger) CreateTextWriter(w io.Writer) *LoggerTextWriter {
 	return CreateTextWriter(w, l.printTraceback, l.printTime)
 }
+// CreateTextStdoutWriter creates a non-owning text writer for os.Stdout.
 func (l *Logger) CreateTextStdoutWriter() *LoggerTextWriter {
 	return CreateTextStdoutWriter(l.printTraceback, l.printTime)
 }
+// CreateTextFileWriter creates an owning text writer for a file.
 func (l *Logger) CreateTextFileWriter(filename string) (*LoggerTextWriter, error) {
 	return CreateTextFileWriter(filename, l.printTraceback, l.printTime)
 }
+// CreateJsonWriter wraps an external writer with the logger JSON settings.
 func (l *Logger) CreateJsonWriter(w io.Writer) *LoggerJsonWriter {
 	return CreateJsonWriter(w, l.jsonPretty)
 }
+// CreateJsonStdoutWriter creates a non-owning JSON writer for os.Stdout.
 func (l *Logger) CreateJsonStdoutWriter() *LoggerJsonWriter {
 	return CreateJsonStdoutWriter(l.jsonPretty)
 }
+// CreateJsonFileWriter creates an owning JSON writer for a file.
 func (l *Logger) CreateJsonFileWriter(filename string) (*LoggerJsonWriter, error) {
 	return CreateJsonFileWriter(filename, l.jsonPretty)
 }
 
+// FormatTime converts time to the package text log timestamp format.
 func FormatTime(t time.Time) string {
 	return fmt.Sprintf("%02d.%02d.%02d %02d:%02d:%02d", t.Day(), t.Month(), t.Year(), t.Hour(), t.Minute(), t.Second())
 }
+// FormatTraceback converts a traceback frame to a compact string.
 func FormatTraceback(mt *MethodTraceback) string {
 	return fmt.Sprintf("%s:%s:%d", mt.Filename, mt.Method, mt.Line)
 }
+// FormatFullTraceback joins multiple traceback frames into one string.
 func FormatFullTraceback(tracebacks []*MethodTraceback) string {
 	formatted := make([]string, 0)
 	for _, tb := range tracebacks {
@@ -124,6 +153,7 @@ func FormatFullTraceback(tracebacks []*MethodTraceback) string {
 	}
 	return strings.Join(formatted, "->")
 }
+// BuildString renders a text log record using the provided settings.
 func BuildString(level LogLevel, prefix string, printTime, printTraceback bool, m ...any) string {
 	args := []string{
 		fmt.Sprintf("[%s]", prefix),

logger_test.go

@@ -0,0 +1,215 @@
+package slog
+
+import (
+	"bytes"
+	"errors"
+	"os"
+	"strings"
+	"testing"
+)
+
+type stubLoggerWriter struct {
+	printErr   error
+	closeErr   error
+	printCalls int
+	closeCalls int
+}
+
+func (w *stubLoggerWriter) Close() error {
+	w.closeCalls++
+	return w.closeErr
+}
+
+func (w *stubLoggerWriter) Write(p []byte) (int, error) {
+	return len(p), nil
+}
+
+func (w *stubLoggerWriter) Print(_ LogLevel, _ string, _ []*MethodTraceback, _ ...any) error {
+	w.printCalls++
+	return w.printErr
+}
+
+func TestLoggerCloseReturnsJoinedErrorsWithoutRelogging(t *testing.T) {
+	firstErr := errors.New("first close failed")
+	secondErr := errors.New("second close failed")
+	first := &stubLoggerWriter{closeErr: firstErr}
+	second := &stubLoggerWriter{closeErr: secondErr}
+
+	logger := CreateLogger().AddWriters(first, second)
+	err := logger.Close()
+	if !errors.Is(err, firstErr) {
+		t.Fatalf("Close() error should include first writer error, got %v", err)
+	}
+	if !errors.Is(err, secondErr) {
+		t.Fatalf("Close() error should include second writer error, got %v", err)
+	}
+	if first.printCalls != 0 || second.printCalls != 0 {
+		t.Fatalf("Close() should not log through writers again, got print calls first=%d second=%d", first.printCalls, second.printCalls)
+	}
+	if first.closeCalls != 1 || second.closeCalls != 1 {
+		t.Fatalf("Close() should close each writer once, got close calls first=%d second=%d", first.closeCalls, second.closeCalls)
+	}
+	if err := logger.Close(); err != nil {
+		t.Fatalf("second Close() should be a no-op, got %v", err)
+	}
+}
+
+func TestLoggerPrintDoesNotRecurseOnWriterError(t *testing.T) {
+	oldStderr := os.Stderr
+	stderrFile, err := os.CreateTemp(t.TempDir(), "stderr")
+	if err != nil {
+		t.Fatalf("CreateTemp() error = %v", err)
+	}
+	os.Stderr = stderrFile
+	t.Cleanup(func() {
+		os.Stderr = oldStderr
+		_ = stderrFile.Close()
+	})
+
+	bad := &stubLoggerWriter{printErr: errors.New("print failed")}
+	good := &stubLoggerWriter{}
+
+	logger := CreateLogger().AddWriters(bad, good)
+	logger.Error("boom")
+
+	if bad.printCalls != 1 {
+		t.Fatalf("bad writer should be called once, got %d", bad.printCalls)
+	}
+	if good.printCalls != 1 {
+		t.Fatalf("good writer should be called once, got %d", good.printCalls)
+	}
+}
+
+func TestCreateTextWriterCloseOnNonCloserIsNoOp(t *testing.T) {
+	writer := CreateTextWriter(&bytes.Buffer{}, false, false)
+	if err := writer.Close(); err != nil {
+		t.Fatalf("Close() error = %v", err)
+	}
+}
+
+func TestCreateTextWriterDoesNotCloseExternalCloser(t *testing.T) {
+	file, err := os.CreateTemp(t.TempDir(), "text-writer")
+	if err != nil {
+		t.Fatalf("CreateTemp() error = %v", err)
+	}
+	t.Cleanup(func() {
+		_ = file.Close()
+	})
+
+	writer := CreateTextWriter(file, false, false)
+	if err := writer.Close(); err != nil {
+		t.Fatalf("Close() error = %v", err)
+	}
+	if _, err := file.WriteString("still open"); err != nil {
+		t.Fatalf("CreateTextWriter() should not close external writers, got %v", err)
+	}
+}
+
+func TestCreateJsonWriterCloseOnNonCloserIsNoOp(t *testing.T) {
+	writer := CreateJsonWriter(&bytes.Buffer{}, false)
+	if err := writer.Close(); err != nil {
+		t.Fatalf("Close() error = %v", err)
+	}
+}
+
+func TestCreateJsonWriterDoesNotCloseExternalCloser(t *testing.T) {
+	file, err := os.CreateTemp(t.TempDir(), "json-writer")
+	if err != nil {
+		t.Fatalf("CreateTemp() error = %v", err)
+	}
+	t.Cleanup(func() {
+		_ = file.Close()
+	})
+
+	writer := CreateJsonWriter(file, false)
+	if err := writer.Close(); err != nil {
+		t.Fatalf("Close() error = %v", err)
+	}
+	if _, err := file.WriteString("still open"); err != nil {
+		t.Fatalf("CreateJsonWriter() should not close external writers, got %v", err)
+	}
+}
+
+func TestCreateTextStdoutWriterDoesNotCloseStdout(t *testing.T) {
+	stdoutFile := swapStdout(t)
+
+	writer := CreateTextStdoutWriter(false, false)
+	if err := writer.Close(); err != nil {
+		t.Fatalf("Close() error = %v", err)
+	}
+	if _, err := stdoutFile.WriteString("still open"); err != nil {
+		t.Fatalf("stdout writer Close() should not close stdout, got %v", err)
+	}
+}
+
+func TestCreateJsonStdoutWriterDoesNotCloseStdout(t *testing.T) {
+	stdoutFile := swapStdout(t)
+
+	writer := CreateJsonStdoutWriter(false)
+	if err := writer.Close(); err != nil {
+		t.Fatalf("Close() error = %v", err)
+	}
+	if _, err := stdoutFile.WriteString("still open"); err != nil {
+		t.Fatalf("stdout writer Close() should not close stdout, got %v", err)
+	}
+}
+
+func TestGetFullTracebackSkipsRuntimeAndSlogFrames(t *testing.T) {
+	tracebacks := captureTracebackForTest()
+	if len(tracebacks) == 0 {
+		t.Fatal("expected at least one traceback frame")
+	}
+
+	first := tracebacks[0]
+	if first.Method != "captureTracebackForTest" {
+		t.Fatalf("first frame should be the nearest user frame, got %s", first.Method)
+	}
+	for _, tb := range tracebacks {
+		if strings.HasPrefix(tb.Signature, "runtime.") {
+			t.Fatalf("runtime frame should be filtered out, got %s", tb.Signature)
+		}
+		if _, ok := internalTracebackMethods[tb.Method]; ok {
+			t.Fatalf("internal slog frame should be filtered out, got %s", tb.Signature)
+		}
+	}
+}
+
+func TestGetTracebackReturnsNearestUserFrame(t *testing.T) {
+	tb := captureSingleTracebackForTest()
+	if tb == nil {
+		t.Fatal("expected traceback frame")
+	}
+	if tb.Method != "captureSingleTracebackForTest" {
+		t.Fatalf("expected nearest user frame, got %s", tb.Method)
+	}
+	if strings.HasPrefix(tb.Signature, "runtime.") {
+		t.Fatalf("runtime frame should be filtered out, got %s", tb.Signature)
+	}
+	if _, ok := internalTracebackMethods[tb.Method]; ok {
+		t.Fatalf("internal slog frame should be filtered out, got %s", tb.Signature)
+	}
+}
+
+func swapStdout(t *testing.T) *os.File {
+	t.Helper()
+
+	oldStdout := os.Stdout
+	stdoutFile, err := os.CreateTemp(t.TempDir(), "stdout")
+	if err != nil {
+		t.Fatalf("CreateTemp() error = %v", err)
+	}
+	os.Stdout = stdoutFile
+	t.Cleanup(func() {
+		os.Stdout = oldStdout
+		_ = stdoutFile.Close()
+	})
+	return stdoutFile
+}
+
+func captureTracebackForTest() []*MethodTraceback {
+	return getFullTraceback(0)
+}
+
+func captureSingleTracebackForTest() *MethodTraceback {
+	return getTraceback()
+}

traceback.go

@@ -2,59 +2,83 @@ package slog
 
 import (
 	"runtime"
-	"sort"
 	"strings"
 )
 
-func getTraceback() *MethodTraceback {
-	caller, _, _, _ := runtime.Caller(5)
-	details := runtime.FuncForPC(caller)
-	signature := details.Name()
-	path, line := details.FileLine(caller)
-	splitPath := strings.Split(path, "/")
-
-	splitSignature := strings.Split(signature, ".")
-	method := splitSignature[len(splitSignature)-1]
-
-	tb := &MethodTraceback{
-		Filename:  splitPath[len(splitPath)-1],
-		FullPath:  path,
-		Line:      line,
-		Signature: signature,
-		Method:    method,
-	}
-
-	return tb
+var internalTracebackMethods = map[string]struct{}{
+	"Infof":             {},
+	"Info":              {},
+	"Infoln":            {},
+	"Warnf":             {},
+	"Warn":              {},
+	"Warnln":            {},
+	"Errorf":            {},
+	"Error":             {},
+	"Errorln":           {},
+	"Fatalf":            {},
+	"Fatal":             {},
+	"Fatalln":           {},
+	"Debugf":            {},
+	"Debug":             {},
+	"Debugln":           {},
+	"print":             {},
+	"println":           {},
+	"reportWriterError": {},
+	"getTraceback":      {},
+	"getFullTraceback":  {},
 }
+
+func getTraceback() *MethodTraceback {
+	tracebacks := getFullTraceback(0)
+	if len(tracebacks) == 0 {
+		return nil
+	}
+	return tracebacks[0]
+}
+
 func getFullTraceback(skip int) []*MethodTraceback {
 	pc := make([]uintptr, 15)
-	runtime.Callers(skip, pc)
+	n := runtime.Callers(skip+2, pc)
 	list := make([]*MethodTraceback, 0)
-	frames := runtime.CallersFrames(pc)
+	frames := runtime.CallersFrames(pc[:n])
 	for {
 		frame, more := frames.Next()
+		tb := buildMethodTraceback(frame.PC)
+		if tb != nil && !isInternalTraceback(tb) {
+			list = append(list, tb)
+		}
 		if !more {
 			break
 		}
-		details := runtime.FuncForPC(frame.PC)
-		signature := details.Name()
-		path, line := details.FileLine(frame.PC)
-		splitPath := strings.Split(path, "/")
+	}
+	return list
+}
 
+func buildMethodTraceback(pc uintptr) *MethodTraceback {
+	details := runtime.FuncForPC(pc)
+	if details == nil {
+		return nil
+	}
+
+	signature := details.Name()
+	path, line := details.FileLine(pc)
+	splitPath := strings.Split(path, "/")
 	splitSignature := strings.Split(signature, ".")
 	method := splitSignature[len(splitSignature)-1]
 
-		tb := &MethodTraceback{
+	return &MethodTraceback{
 		Filename:  splitPath[len(splitPath)-1],
 		FullPath:  path,
 		Line:      line,
 		Signature: signature,
 		Method:    method,
 	}
-		list = append(list, tb)
-	}
-	sort.Slice(list, func(i, j int) bool {
-		return j < i
-	})
-	return list
+}
+
+func isInternalTraceback(tb *MethodTraceback) bool {
+	if strings.HasPrefix(tb.Signature, "runtime.") {
+		return true
+	}
+	_, ok := internalTracebackMethods[tb.Method]
+	return ok
 }

utils.go

@@ -1,5 +1,6 @@
 package slog
 
+// Map applies f to each element of s and returns the resulting slice.
 func Map[T, R any](s []T, f func(T) R) []R {
 	out := make([]R, len(s))
 	for i, el := range s {

writers.go

@@ -1,7 +1,6 @@
 package slog
 
 import (
-	"bufio"
 	"encoding/json"
 	"fmt"
 	"io"
@@ -11,42 +10,51 @@ import (
 	"time"
 )
 
+// LoggerWriter is the common sink interface used by Logger.
 type LoggerWriter interface {
 	Close() error
 	Write(p []byte) (n int, err error)
 	Print(level LogLevel, prefix string, traceback []*MethodTraceback, messages ...any) error
 }
 
+// LoggerTextWriter writes human-readable log records to an io.Writer.
 type LoggerTextWriter struct {
 	LoggerWriter
 	writer         io.Writer
+	closer         io.Closer
 	printTraceback bool
 	printTime      bool
 }
 
+// Write forwards raw bytes to the underlying writer.
 func (w *LoggerTextWriter) Write(p []byte) (n int, err error) {
-	n, err = w.writer.Write(p)
-	if err != nil {
-		return n, err
-	}
-	err = bufio.NewWriter(w.writer).Flush()
-	return n, err
+	return w.writer.Write(p)
 }
+
+// Print formats the provided record as text and writes it to the underlying writer.
 func (w *LoggerTextWriter) Print(level LogLevel, prefix string, _ []*MethodTraceback, messages ...any) error {
 	s := BuildString(level, prefix, w.printTime, w.printTraceback, messages...)
 	_, err := w.Write([]byte(s))
 	return err
 }
+
+// Close closes the owned writer, if any.
 func (w *LoggerTextWriter) Close() error {
-	return w.writer.(io.Closer).Close()
+	if w.closer == nil {
+		return nil
+	}
+	return w.closer.Close()
 }
 
-// LoggerJsonWriter write into writer JSON
+// LoggerJsonWriter writes structured log records as JSON.
 type LoggerJsonWriter struct {
 	LoggerWriter
 	writer io.Writer
+	closer io.Closer
 	pretty bool
 }
+
+// LoggerJsonMessage is the JSON payload emitted by LoggerJsonWriter.
 type LoggerJsonMessage struct {
 	Time      time.Time          `json:"time"`
 	Level     string             `json:"level"`
@@ -55,23 +63,28 @@ type LoggerJsonMessage struct {
 	Traceback []*MethodTraceback `json:"traceback"`
 }
 
+// Write forwards raw bytes to the underlying writer.
 func (w *LoggerJsonWriter) Write(data []byte) (int, error) {
-	n, err := w.writer.Write(data)
-	if err != nil {
-		return n, err
-	}
-	err = bufio.NewWriter(w.writer).Flush()
-	return n, err
+	return w.writer.Write(data)
 }
+
+// Print encodes the provided record as JSON and writes it to the underlying writer.
 func (w *LoggerJsonWriter) Print(level LogLevel, prefix string, traceback []*MethodTraceback, messages ...any) error {
 	msg := Map(messages, func(el any) string {
 		return fmt.Sprintf("%v", el)
 	})
+
+	newline := false
+	if msg[len(msg)-1] == "\n" {
+		newline = true
+		msg = msg[:len(msg)-1]
+	}
+
 	m := LoggerJsonMessage{
 		Time:      time.Now(),
 		Level:     level.GetName(),
 		Prefix:    prefix,
-		Message:   strings.Join(msg, " "),
+		Message:   strings.TrimSpace(strings.Join(msg, " ")),
 		Traceback: traceback,
 	}
 	var data []byte
@@ -84,19 +97,32 @@ func (w *LoggerJsonWriter) Print(level LogLevel, prefix string, traceback []*Met
 	if err != nil {
 		return err
 	}
-	_, err = w.Write(append(data, []byte("\n")...))
+	if newline {
+		data = append(data, '\n')
+	}
+	_, err = w.Write(data)
 	return err
 }
+
+// Close closes the owned writer, if any.
 func (w *LoggerJsonWriter) Close() error {
-	return w.writer.(io.Closer).Close()
+	if w.closer == nil {
+		return nil
+	}
+	return w.closer.Close()
 }
 
+// CreateTextWriter wraps an external writer for text output without taking
+// ownership of it.
 func CreateTextWriter(w io.Writer, printTraceback, printTime bool) *LoggerTextWriter {
 	writer := &LoggerTextWriter{
 		writer: w, printTraceback: printTraceback, printTime: printTime,
 	}
 	return writer
 }
+
+// CreateTextFileWriter creates a text writer for path, creating parent
+// directories as needed. The returned writer owns the opened file.
 func CreateTextFileWriter(path string, printTraceback, printTime bool) (*LoggerTextWriter, error) {
 	err := os.MkdirAll(filepath.Dir(path), os.ModePerm)
 	if err != nil {
@@ -106,21 +132,38 @@ func CreateTextFileWriter(path string, printTraceback, printTime bool) (*LoggerT
 	if err != nil {
 		return nil, err
 	}
-	return CreateTextWriter(file, printTraceback, printTime), nil
-}
-func CreateTextStdoutWriter(printTraceback, printTime bool) *LoggerTextWriter {
-	return CreateTextWriter(os.Stdout, printTraceback, printTime)
+	writer := CreateTextWriter(file, printTraceback, printTime)
+	writer.closer = file
+	return writer, nil
 }
 
+// CreateTextStdoutWriter creates a text writer for os.Stdout without taking
+// ownership of stdout.
+func CreateTextStdoutWriter(printTraceback, printTime bool) *LoggerTextWriter {
+	writer := CreateTextWriter(os.Stdout, printTraceback, printTime)
+	writer.closer = nil
+	return writer
+}
+
+// CreateJsonWriter wraps an external writer for JSON output without taking
+// ownership of it.
 func CreateJsonWriter(w io.Writer, pretty bool) *LoggerJsonWriter {
 	writer := &LoggerJsonWriter{
 		writer: w, pretty: pretty,
 	}
 	return writer
 }
+
+// CreateJsonStdoutWriter creates a JSON writer for os.Stdout without taking
+// ownership of stdout.
 func CreateJsonStdoutWriter(pretty bool) *LoggerJsonWriter {
-	return CreateJsonWriter(os.Stdout, pretty)
+	writer := CreateJsonWriter(os.Stdout, pretty)
+	writer.closer = nil
+	return writer
 }
+
+// CreateJsonFileWriter creates a JSON writer for path, creating parent
+// directories as needed. The returned writer owns the opened file.
 func CreateJsonFileWriter(path string, pretty bool) (*LoggerJsonWriter, error) {
 	err := os.MkdirAll(filepath.Dir(path), os.ModePerm)
 	if err != nil {
@@ -130,5 +173,7 @@ func CreateJsonFileWriter(path string, pretty bool) (*LoggerJsonWriter, error) {
 	if err != nil {
 		return nil, err
 	}
-	return CreateJsonWriter(file, pretty), nil
+	writer := CreateJsonWriter(file, pretty)
+	writer.closer = file
+	return writer, nil
 }